Quilombo Driven Development

liftP.js

const wait = n => new Promise(res => setTimeout(res, n));
const log = console.log.bind(console);

const dummy = payload => wait(1000).then(() => payload);

const user = () => (log('user'), dummy({user: 'john'}));
const tweets = () => (log('tweets'), dummy({tweets: ['asdasd', 'dsada']}));
const github = () => (log('github'), dummy({repos: ['asdasd', 'dsada']}));

// buildResult   :: (user, tweets, github) -> {user, tweets, github}
const buildResult = (user, tweets, github) => ({user, tweets, github});

// Promise.all :: [Promise(*)] -> Promise([*])

function fetchResult() {
    return Promise.all([user(), tweets(), github()])
        .then(([user, tweets, github]) => buildResult(user, tweets, github));
}

// buildResult'  :: (Promise(user), Promise(tweets), Promise(github)) -> Promise({user, tweets, github})

function buildResult2(userP, tweetsP, githubP) {
    return Promise.all([userP, tweetsP, githubP])
        .then(([user, tweets, github]) => buildResult(user, tweets, github));
}

function buildResult3(...args) {
    return Promise.all(args)
        .then(args => buildResult(...args));
}

function fetchResult2() {
    return buildResult2(user(), tweets(), github());
}

function fetchResult3() {
    return buildResult3(user(), tweets(), github());
}

// 

const liftP = fn => (...args) => Promise.all(args).then(args => fn(...args));

function fetchResultsLift() {
    return liftP(buildResult)(user(), tweets(), github());
}